The built-in function IO.ANSI.escape will insert ANSI escape sequences in a string. If you put the resulting strings into a terminal, you can a dd colors and bold or underlined text. Explore the library, and then use it to colorize our tracing's output.
See the colorize.exs file for the full module.
I've looked through the 1.1, 1.2, and 1.3 docs and IO.ANSI definitely doesn't have an escape function; however, the module does contain a number of other coloration functions so I will use those instead.
Lets make the calls blue and the results green:
IO.puts "#{IO.ANSI.blue}==> call: #{Tracer.dump_defn(unquote(name), unquote(args))}"
result = unquote(content)
IO.puts "#{IO.ANSI.green}<== result: #{result}"
I doubt colors will show up in markdown but it works!